A variety of processes for production of specific alkylaromatic compounds are currently practiced in industry. Many such processes involve an alkylation step to produce the desired alkylaromatic compound and a separate transalkylation step to convert the undesired by-products back to reactants for recycle to the alkylation process. Processes for producing specific desired isomers of alkylaromatic compounds are generally more complex. Examples of desired isomers of alkylaromatic compounds are meta-diisopropylbenzene and para-diisopropylbenzene.
In typical processes for the production of diisopropylbenzenes (DIPBs), cumene is alkylated with propylene in the presence of an alkylation catalyst under reaction conditions suitable for the production of DIPBs. Typically, a particular facility does not have use for all of the products of the alkylation reaction, and the undesired byproducts are generally transalkylated with a benzene co-feed to produce cumene for recycle to the alkylation reactor. Meta- and para-DIPB are important intermediates in organic synthesis of resorcinol and hydroquinone, respectively.
DIPB can also be produced by separation from the polyalkylated by-product of the alkylation of benzene with propylene to produce cumene. However, DIPB separated from the polyalkylated fraction of current commercial cumene plants is rich in the kinetically preferred para- and ortho-DIPB isomers, making this route of limited use in the synthesis of meta-DIPB.
The term “transalkylation” is generally used to mean the exchange of alkyl substituent groups between aromatic hydrocarbons. The aromatic hydrocarbons can comprise a single alkyl substituted aromatic hydrocarbon or a mixture of aromatic hydrocarbons, provided that in the case of a mixture at least one of the components is an alkyl substituted aromatic hydrocarbon. A common transalkylation reaction is the reaction of a dialkylaromatic with benzene to produce a monoalkylaromatic product. Other examples of transalkylation reactions include disproportionation and isomerization.
U.S. Pat. No. 2,848,514 discloses a process for producing DIPBs including isomerization of ortho-, meta-, and optionally para-DIPB over a cracking catalyst to obtain a stream with less than 5% ortho- as a percentage of total DIPBs and also transalkylating polyisopropylbenzenes with benzene and/or cumene over a cracking catalyst to obtain a stream with less than 5% ortho- as a percentage of total DIPBs.
U.S. Pat. No. 3,763,259 discloses a process for producing DIPBs including disproportionating cumene with polyisopropylbenzenes and isomerization of the disproportionation product with ortho-and meta-DIPB. The disproportionation catalyst is a boron halide-modified inorganic oxide or a crystalline alumino-silicate.
GB Patent No. 755,956 discloses a process in which para-DIPB is prepared by isomerization of ortho- and meta-DIPB by heating with boron or aluminum halides and by transalkylation of higher alkylated products with benzene or cumene, also by heating with boron or aluminum halides.
GB Patent No. 786,305 discloses a process in which para-DIPB is prepared by isomerization of ortho- and meta-DIPB with an aluminum silicate catalyst comprising 85-90% SiO2, 10-15% Al2O3, and 0.1-0.2% H2O.
U.S. Pat. No. 4,375,575 discloses isomerization of DIPBs over a catalyst prepared by impregnating dehydrated amorphous silica gel with aluminum hydride.
NL Patent No. 85,204 discloses a process for transalkylating di-, tri-, or polyisopropylbenzenes with benzene and/or cumene over an aluminum silicate catalyst containing 0.1-0.2 wt. % water.
U.S. Pat. No. 4,822,943, which is herein fully incorporated by reference, discloses a process for the selective production of para-DIPB by reacting cumene and/or benzene with propylene over the molecular sieve ZSM-12.
U.S. Pat. No. 5,329,059, which is herein fully incorporated by reference, discloses a process for the disproportionation of an alkylaromatic compound, wherein the alkyl group has from 1 to about 6 carbon atoms, e.g., cumene, by contacting said compound with catalyst comprising an active form of synthetic porous crystalline MCM-49.
U.S. Pat. No. 6,049,018, which is herein fully incorporated by reference, discloses the porous crystalline material MCM-68 and its use in the alkylation of aromatics with short chain (C2-C6) olefins (for example, the alkylation of benzene with ethylene or propylene to produce ethylbenzene or cumene respectively), the transalkylation of aromatics (for example, the transalkylation of polyethylbenzenes or polyisopropylbenzenes with benzene to produce ethylbenzene or cumene respectively), and the disproportionation of alkylaromatics (for example, the disproportionation of toluene to produce xylenes).
In one process for production of p-DIPB, cumene is alkylated with propylene to produce mixed DIPBs, the para-DIPB is separated out, benzene is co-fed with meta- and ortho-DIPB to a reactor containing MCM-22 where transalkylation takes place, and the resulting cumene product is recycled to the alkylation reactor and re-alkylated with propylene to form mixed DIPBs. The para-DIPB is separated and the meta- and ortho-DIPB are recycled to the transalkylation reactor.
Although the feedstocks for alkylbenzene production generally include benzene, the handling of benzene is subject to numerous safety and environmental restrictions, making its use as a feedstock less desirable from a safety, environmental, and economic perspective.